Preserving frozen ground with active cooling under seasonal forcing—An experimental study

Global warming is degrading mountain permafrost, threatening infrastructure such as buildings, cable cars, avalanche protection structures, and tunnels. Degradation is mainly driven by increased air temperatures, but liquid precipitation at high elevations also contributes. Cooling systems for thermal stabilisation, which delay permafrost degradation, are not widely used in Europe and must be tested under various conditions before their successful implementation. We designed and built a portable autonomous demonstrator to simulate thermal and other energy transfer processes using active cooling. The physical model consists of a substrate in a thermally insulated box with a horizontal array of cooling pipes to create a frozen layer, the cooling system, photovoltaic panels, and a battery. First, the impact of liquid precipitation on the ground sample was investigated in a climate chamber with scenarios representative of winter and summer conditions. The results show that rainfall causes the partial thawing of the frozen layer on the surface. During winter conditions, warm precipitation caused an increase in the temperature of the frozen layer to 0 °C. However, during summer conditions with applied active cooling, rainfall can also promote transient thickening of the frozen layer by up to 25% through refreezing that leads to frost heave, underlining the need for precipitation mitigation. The demonstrator was then placed outdoors during the summer to investigate the persistence of the protective thermal barrier layer under atmospheric forcing powered only by solar energy. The thermal barrier layer remained stable for all 6 months of the experiments. Controlling frozen-layer thickness helped quantify heat fluxes and highlighted the interplay of atmospheric forcing, solar radiation, and cooling efficiency. Parametric analysis shows that solar panel and battery size can be balanced to meet compressor demand, with energy use scaling with solar radiation and air temperature. This demonstrates the feasibility of adaptive solar-powered permafrost cooling and dynamic energy management. This demonstrator proved useful for understanding the response of the ground to active cooling and provides information for designing and deploying systems that improve infrastructure resilience in mountain regions such as the Swiss Alps.